The present invention relates to the use of vinylaromatic-diene copolymers in lactam compositions. The invention also relates to lactam melts which comprise random vinylaromatic-diene copolymers. The invention further relates to the production of lactam melts, and also to use of these, preferably in the field of activated anionic lactam polymerization, e.g. for producing cast polyamides.
Vinylaromatic-diene copolymers of varying structure, an example being styrene-butadiene copolymers, have been known for many years. They can be used as additions for producing various molding compositions. The random vinylaromatic-diene copolymers used in the invention include, in their structure, at least one section which comprises a diene and a vinylaromatic randomly distributed. These copolymers can be produced by processes known from the literature, see by way of example EP-A 0 766 706 and EP-A 0 859 803.
DE-A 44 20 952 describes elastomeric block copolymers which are composed of at least one block A which forms a hard phase made of styrene, and of a block B which forms an elastomeric soft phase and which comprises butadiene, and of at least one elastomeric block B/A comprising styrene and butadiene. The ratio of block A to block B/A here is important.
Various processes for producing polyamides have been known for many years. Typical polyamides are semicrystalline and amorphous polyamide resins with a molar mass of at least 5000 g/mol, these usually being termed nylon. Polyamides of this type are described by way of example in U.S. Pat. Nos. 2,512,606 and 3,393,210.
Polyamides can be produced firstly via condensation of equimolar amounts of a saturated or aromatic dicarboxylic acid with a saturated or aromatic diamine, or else via condensation of ω-aminocarboxylic acids or via polyaddition of corresponding lactams. Typical examples of polyamides are polyhexamethyleneadipamide (nylon-6,6), and also the polyamide polycaprolactam, which is obtained via ring-opening of lactams.
Activated anionic polymerization of lactams for producing polyamides is a process having very sensitive chemistry, and many additives disrupt this process. By way of example, conventional thickeners for adjusting viscosity, e.g. polyacrylamides, are disadvantageous for the polymerization reaction or have low solubility in the lactam melts.
Production of polyamide moldings via activated anionic lactam polymerization is described as early as in 1966 in Kunststoff-Handbuch [Plastics handbook] (volume VI, Polyamide [Polyamides], Carl-Hanser-Verlag, 1966), where other impact modifiers are also added in order to improve the strength of the polyamide moldings. The impact modifiers used are in particular polyalkylene glycols (see J. L. M. van der Loos, ACS Symposium Series 1985, 270, 181-191). There are various types of impact modifiers here, examples being those which interact with the molecular structure of the polymers (e.g. polyalkylene glycols and polyetheramines), and also those which do not interact with the molecular structure of the polymers but instead form a mixture (or a blend) with the polymer.